This application claims the priority benefit of Taiwan application serial no. 89126332, filed Dec. 11, 2000.
1. Field of Invention
The present invention relates to a display device. More particularly, the present invention relates to a structure of a storage capacitor on common (Cst on Common.)
2. Description of Related Art
A display is a commonly-used device, especially the use of a display required in a television or a computer. Normally, a cathode ray tube is used in design for the display, but it requires a large area. A notebook computer particularly cannot use the display with cathode ray tube design. Therefore, a planar display of a pixel-matrix product, such as a liquid crystal display (LCD) or a thin film transistor liquid crystal display (TFT-LCD,) has been successfully introduced in the market. Image of the TFT-LCD is composed by the pixel matrix. Each pixel is controlled by a thin film transistor.
As a larger display area of TFT-LCD is desired, it is a trend to design the pixel with the type of Cst on Common for reducing the affection of the gate delay on driving the TFT-LCD. In this design manner, the common electrode and the gate electrode are separately formed. When a fabrication residual matter remains near the capacitor the residual matter may cause a short circuit and causes a defect of bright spot on the pixel. In this situation, a laser is usually used to remove the residual matter when the residual matter remains, and this may also open the common electrode line, causing a gate undertone line. In order to avoid the undertone line, the current method tends not to repair the defect of the bright spots when it occurs on the capacitor. This causes the existence of the bright spots in the display device.
However, the current market requires that a display have the best image quality. The main trend for fabricating the LCD is thus forming a non-bright spot by using the technique of laser repair and changing the bright spot to a dark spot. The current technique of laser repair cannot make a fully dark spot, because the latest technique of forming the dark spot will also cause a defect of the light line due to a short circuit between the common electrode and the gate electrode. Therefore, an important key to improving image quality is solving the defect points of the storage capacitor.
The invention provides a structure of a capacitor. The structure allows a dark spot process to be performed without causing an undertone line.
As embodied and broadly described herein, the invention provides a structure of a capacitor that is connected to a capacitor switch element. The structure of the storage capacitor on common includes a first capacitor electrode, a capacitor dielectric layer, a second capacitor electrode and a redundant pattern. The first capacitor electrode is a common electrode line connected to the capacitor switch element. The capacitor dielectric layer is located on the common electrode line. The second capacitor electrode is located on the capacitor dielectric layer. Therefore, a capacitor is formed by the first capacitor electrode and the second capacitor electrode and the capacitor dielectric layer. The redundant pattern has two ends and both two ends are connected to the common electrode line. The common electrode line can maintain the conducting state without open circuit due to the redundant pattern when the defective capacitor is cut and separated.
When the dark spot process is performed, the capacitor having defect can be cut and separated. Since the redundant pattern is connected to both ends of the capacitor that is cut and separated, the conducting state of the whole common electrode line remains. As a result, an open common electrode line is prevented from occurring, and therefore the gate undertone line is avoided. The image quality is improved.
In the above, the capacitor switch element includes a thin film transistor that is used on a liquid crystal display.
The design of the redundant pattern of this invention can easily achieve the objective of a non-bright spot; therefore the image quality is further improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.